Severe Weather Threat Day 2 Sun Sep 1

Downstream Of A Closed Low Embedded Within An Amplified Upper Trough Slowly Approaching The Pacific Coast...Models Indicate SomeBroadening Of Anticyclonic Mid/Upper Flow During This Period...FromThe Northern Intermountain Region Across The Canadian/U.S. Border Area...Through The Northern Plains And Portions Of The Upper Mississippi Valley. As This Occurs...Further Amplification Of ATrough Farther Downstream Appears Possible...Before It GraduallyTurns Eastward Across The Lower Great Lakes Region By 12z Monday.

Models Suggest That A Series Of Low-Level Cool/Dry Intrusions WillAccompany This Feature Into The North Central U.S...Before Eventually Consolidating And Progressing Southward Into The Central Plains...And Across Middle Mississippi Valley And Upper Midwest.

While Seasonably High Moisture Content Air Will Linger Along AndSouth Of An Initial Weakening Front Across Parts Of The Ohio Valley Into Middle And Northern Atlantic Coastal Areas...Another Corridor Of Increasing Moisture Appears Likely Across The Central Plains/Lower Missouri Valley Into Portions Of The Upper Mississippi Valley By 12z Sunday.

Although Mid-Level Lapse Rates By This Time Are Not Expected To BeEspecially Steep To The Northeast And East Of The Central Plains... Guidance Indicates That The Moisture Will Be Supportive Of Moderately Large Cape Where Early Day Convection Does Not InhibitSurface Heating. This Probably Will Support Considerable ConvectiveDevelopment Sunday Into Sunday Night.

Additional Thunderstorm Activity Appears Likely In Association WithMonsoonal Moisture Across Much Of The Four Corners Region Into The Great Basin. Northward Advection Of Moisture Into The Northern Intermountain Region Is Still Expected To Support IncreasingPotential For Thunderstorms...But Probabilities/Coverage May Remain Fairly Low/Sparse.

Upper Midwest Into Great Lakes Region...

Uncertainties Remain Concerning Convective Potential Across TheRegion For This Period. Cloud Cover/Precipitation Associated WithRemnant Early Day Convection May Inhibit Destabilization AcrossParts Of Eastern Iowa Into Wisconsin...And Boundary Layer MoistureTo The East...Across Northern Illinois Into Michigan May Still Be InThe Process Of Recovering From The Prior Front. However... Moistening Is Expected As The Primary Surface Cyclone Shifts East Northeast Of The Upper Great Lakes Region During The Day.

Most Guidance Now Indicates That A Fairly Significant SecondaryImpulse Associated With The Amplifying Upper Trough Will DigSoutheast Of The Upper Mississippi Valley...Across Wisconsin By Late Afternoon...Into Lower Michigan During The Evening. AlthoughLow-Level Wind Fields And Shear Are Expected To Remain Weak... Deep Layer Shear Beneath 30-40+ Kt West Northwesterly 500 Mb Flow...Along With Mid-Level Cooling And Large-Scale Ascent Associated With The Impulse...May Contribute To Storm Development With At Least Low Severe Hail/Wind Potential.

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